Many attempts to combine the bulk-generating benefit of throughdrying with the dewatering efficiency of wet-pressing have been disclosed over the past 20 years. An exemplary process is disclosed in U.S. Pat. No. 6,287,426. A typical process utilizes a high pressure dewatering nip formed between a felt and an impermeable belt to increase the wet web consistency to about 35 to 50 percent. The web adheres to and follows the impermeable belt as it exits the press nip. The dewatered web is then transferred to a structuring fabric with the aid of a vacuum roll to impart texture to the web prior to drying.
Transfer belts having a regular or uniform grooved micro-structure on their surface running in the machine direction have been used for transferring a web from a press felt to a further downstream process. The grooved belt is compressed flat in the dewatering press nip, allowing the dewatered web to transfer to the belt, but then rebounds to its natural grooved state soon after leaving the press. While effective for relatively heavy basis weight webs, the use of such modified belts still is not effective for processing light-weight tissue webs at high speeds necessary for commercial applications because of the difficulty associated with transferring low basis weight wet webs, which have virtually no strength. A wet tissue web will not naturally make such a transfer because there is a thin water film between the tissue web and the belt surface that generates a high adhesion force between the two materials. Attempts to remove the fragile tissue web from the belt surface often result in torn webs.
Therefore, there is a need for an efficient method of making wet-pressed paper webs at high speeds. This method is especially useful for the production of un-creped through air dried paper. AS would be appreciated, through air dried paper requires a significant amount of energy to dry. By pre-pressing the paper with the disclosed method, a significant amount of water is removed by mechanical means, thus reducing the thermal drying requirements of a through air dried process.